1. The Field of the Invention
The present invention relates generally to lower extremity orthoses. More particularly, it concerns an ankle positioning splint for patients confined to permanent bedrest, or individuals at risk for ankle plantar flexion contractures (heal cord tendon shortening), or individuals with neurologic conditions that have resulted in pathological increases in muscle tone in the lower extremities.
2. The Background Art
Individuals confined to bedrest, even for brief periods of time, are at substantial risk of developing muscle shortening or contractures. It will be appreciated that the human foot tends to plantar flex to a pointed position during periods of rest whereby the foot moves in the plantar-flexion range of motion (see FIG. 5). Plantar-flexion range of motion refers to movement of the foot downward from a neutral position to some position within approximately 60 degrees of the neutral position. The neutral position refers to the foot being positioned at approximately 90 degrees relative to the lower leg.
If plantar-flexion is allowed to occur for longer than 4 to 5 days, the tendons and ligaments shorten, resulting in a contracture of the ankle joint. One resulting problem is that patients who are comatose or otherwise bedridden for long periods of time experience what is known as "ankle plantar flexion contracture", whereby the tendons and ligaments in the leg effectively shorten into their naturally biased contracted position so that the foot cannot dorsiflex appropriately for ambulation, or allow the individual to walk without a great amount of pain.
Athletes or any other active persons, that is individuals who are involved in weekend sports such as tennis or who exercise on a regular basis (especially on an intermittent basis) may experience heal cord tightness and/or plantar fascitis of the feet. Both conditions are usually very painful. Holding the ankle in the neutral or 90 degree position during sleep helps prevent these painful conditions.
The neurologic patient (an individual with a head injury, either traumatic or vascular in nature), or an individual who has suffered a spinal cord injury, often develops what is termed "hyper-tonicity" of certain muscle groups. Such individuals frequently develop hyper plantar flexion of the ankle joint in both legs. Maintaining the ankle in the neutral position can prevent plantar flexion contractures at the ankle in such individuals.
When contracture occurs at the ankle it is difficult if not impossible for the individual to walk. Attempting to walk with ankle plantar flexion contractures is very painful. Walking with ankle plantar flexion contracture also poses a significant risk of tearing the muscle tendons of the calf muscles (medically termed gastroc-soleus complex, or more commonly the Achilles tendon or heel cord).
Conventional treatment of ankle plantar flexion contractures is performed by physical therapists and other caregivers, and is referred to as "passive range of motion". This treatment involves moving the foot or ankle joint periodically and requires a great deal of force. The purpose of the treatment is to stretch the ligaments and tendons to cause the ankle and foot to assume at least the neutral position. The ultimate goal of this therapy is to allow the ankle joint to move into what is known as "dorsi-flexion" range of motion which will allow normal ambulation (i.e. walking). Dorsi-flexion range of motion is the movement of the foot from the neutral position to a position closer to the leg or up toward the leg (see FIG. 5). Dorsi-flexion range of motion normally involves approximately 20 degrees of movement. Unfortunately, performing passive range of motion on a contractured joint poses a risk of tearing or otherwise damaging the tendons and ligaments in the leg. This treatment approach is very laborious and time consuming and does not always restore the ankle and foot to the neutral position.
It has been discovered that maintaining the foot of a bedridden or neurologic patient in the neutral position inhibits development of contracture. Ankle splint devices have been developed in attempts to hold the foot in the neutral position during periods of bedrest. However, the prior art splint devices are characterized by a number of disadvantages. The natural biasing forces of the foot and leg (and especially the forces caused by hyper tonicity in the neurologic patient) are so great that the foot and leg tend to migrate out of the splint so that the foot returns to its natural biased position anyway. The prior art splint devices have been either ineffective to counteract the muscular forces of the leg, or the straps must be so tight that the patient does not tolerate it or circulation is cut off in the foot and severe pressure sores develop. These problems also hold true for prior art night splints for the athletic conditions of heel cord tightness and plantar fascitis.